Posted
by
samzenpus
on Monday November 02, 2015 @10:00PM
from the getting-the-best-look dept.

TheAlexKnapp writes: Ethan Siegel has written a nice overview of gravitational lensing, and how taking advantage of it has enabled to study parts of the universe that otherwise would've require the construction of massive telescopes. From his Forbes article: "Although the first gravitational lens wasn't discovered for some 40 years after it was first theorized, it's now the most prolific tool for weighing distant (foreground) galaxies, and discovering ultra-distant (background) galaxies. Although this isn't a technique we have precision control over — the Universe puts the lenses and the lensed objects where they are, and all we can do is watch — there's a spectacular amount of material that's out there."

I've been hearing this for ages about how gravitational lenses supposedly allow us to observe anything behind them with great detail, but I've never actually seen a single un-lensed image that would have proved this point.

How would that prove the point? It is quite clear from the observations that galaxies spectroscopically matching ones far away are visible in greater angular resolution and with greater light gathering ability than those that are not gravitationally lensed. If you don't agree with the spectroscopic matching and other observations like star formation regions, etc., then "un-lensing" the image or not is not going to prove anything to you.

Wow, years ago, as a fresh-scrubbed nerd hanging out with other nerds, gravitational lensing was as yet unproven; it was based in science, but I don't think anybody had done it yet.

Of course, this was right around the time when we were on the cusp of seriously discussing exoplanets, yet to confirm a black hole, still working on hubble, and when radio astronomy was still coming into its own. Things which are almost commonplace were cutting edge stuff which hadn't happened yet.

To all the physicists, astrophysicists, amateurs, and other people who have made space discovery so damned awesome for the last few decades... you're fucking awesome, and thanks for showing us just how cool the universe is.

Of course, this was right around the time when we were on the cusp of seriously discussing exoplanets, yet to confirm a black hole, still working on hubble, and when radio astronomy was still coming into its own.

Your sense of time seems a little wonky, since galactic gravitational lensing was late 70s (~60 years after Eddington's original observation using the Sun), radio astronomy was well established by the 60s (e.g. Arecibo was built in 1963), Hubble just got first approval of funds about the same time, and the first confirmed exoplanets was not until the 90s.

Mathematically, both are the same. The gravitational pull causes exactly the same bend than the curved space time. General Relativity says that the gravitational pull you observe is a result of the curved spacetime.

General relativity results in 2x as much bending via gravity as classical theory IIRC

Not for us. The pull of gravity on humans is almost classical theory with the difference being barely detectable as a time dilation. And classical theory allows for gravity to pull on objects going faster than the speed of light while general relativity has no such objects.

Err really no. Photons as packets of light predates very briefly. But e=mc2 *is* relativity, and without that there is no such thing as zero rest mass. That would just be zero mass in *all frames of reference*.

Kinda surprised he'd write an entire article about what a great telescope gravity makes for and not mention the FOCAL [centauri-dreams.org] proposal. If you had a probe sufficiently distant from the sun opposite Alpha Centari and there was a city full of little aliens there, you'd be able to see the cars move around in the streets. Not that this will ever happen or that humanity are capable of such projects - we clearly are not. But it's still a nice idea.

FOCAL is in fact far more plausible than much of the outside of the box thinking. Solar sails can even get you out far enough from the sun. However i am a little suspicious of the diffraction limit claim. It is not really a big lense. Just approximately so, with a massive ball of 6000C plasma in the middle of the camera.